GMC Motorhome: A dash AC discussion

OK, I’m in early, I really wanted to have this discussion on the Dash AC systems in the GMC.  Many of you may know some of this… some maybe all hey, I don’t know but working here with Ruby has brought up how the dash AC evolved.  There were 3 basic dash AC/heat system designs…

Style 1 from 1973-74  This is the system Ruby has being #41 off the assembly… That’s it there in the foreground after being extracted like an abscess tooth from uder the front of Ruby.  And actually if you look at any year coach this part looks the same  .

Maybe they should have scrapped this part too but the differences in the style 2 (1975-6) and the style 3 (19777-8) was in the ducting system. 

The first design is said to have 14 90 degree bends in the ducting system!  The higher you turned the blower the more air block you created!  I say they should have redesigned this box is because even GM was screwing with it even in 1973…. in this #41 coach! 

The firewall was first cut out large then an aluminum plate was riveted in  . then the mating surface on the heater box was rigged up  

The tall baffle to the right that normally opens when the AC comes on is sealed shut!  Yes, this was a prototype… The right wall of it was cut out with a nibbler…. there’s 3 obtuse bends right there.  Then the blower on the left side blows air into this box then shoots it out up through the top of the box….   making a couple more crazy turns THEN it went to the ducting system through the firewall    The baffle door up there causes defrost or vent s to come on.  That’s CRAZY!  So all of you guys…. even you guys with a 77-78 with air actually coming out of all vents may want to pay more attention if you want a good dash AC.

In my mind no matter if you have a style 1..2..or 3, if you are doing a REAL restoration and want to make the dash AC REALLY work… scrap this heater box!  .I try to keep the shop picked up… this heater box is next out with the trash can next to it… well, maybe I’ll keep it … there may be a part I might need… ya never know…

The recirculating duct to the left only has a small hole so that will have to go too.  WOW, look at that!  Getting rid of all that original dash AC/heat control wires and those (what were we thinkin back then) vacuum line system it sure makes for a cleaner underdash.  This will gis me gobbs os space to lay all the new wairing out nice!

So lets move on the the ducting system in the coach…….. maybe lets not!  Crap, we have to…. the ducting system was installed on the back of the plastic dash before the dash was installed.  If you try and take that rotted, brittle plastic dash out…. brother keep a bucked for the pieces!  NO…. don’t do that unless the can of worms you seek is large!

What to do?  There are many companies out there making aftermarket “in dash” AC/heat systems for vintage cars.  Here’s one    As u can see, we HAD actually taken the dash out to mount this system in.  Ender up having to splash a mold of a new dash because as I said… the whole dash came apart in pieces…. Do it if you want…… but I’ve been there!    Still have the mold I think… it was cool … but not real chilly and MAN that was alote of work……. like I said before…don’t do that!

So lets see what we can do with the dash we have… actually you can do a great deal!  Remember the defroster duct was on the top… actually in the right direction, we can seal off that baffle plate and duct the defroster up into the defroster!  Then each dash vent has a box behind it.  seal each box and route a duct from the aftermarket dash to each vent and ..boom…. any year dash will have good air out the vents!

Now before you jump up and rip your dash apart…wait…. all this is theory at this point.  You saw what I tried before….. lets try this and I think the results will not only cost less but be a cleaner job and more classic looking.  KEEP THAT DASH…. get a Mac Dash… this one or his “Mac Daddy”  cause you will need the space.  Better yet, watch us on Ruby    Hope some of this was interesting… stay tuned for more

Hey and thanks for the visit……

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